Mobile electronic devices, such as mobile phones and other mobile devices, are getting smaller. Mobile electronic devices use antennas to receive and transmit information, and the size of the antennas is related to the frequency band being used. For instance half-wavelength and quarter wavelength antennas are commonly used. Typical antennas used in mobile electronic devices include planar inverted F-antenna (PIFA), planar inverted L-antenna (PILA), inverted L-antenna (ILA), inverted F-antenna (IFA), and whip antennas. Many antennas in mobile electronic devices are placed above or in close vicinity to a printed wiring board (PWB) (also called a printed circuit board) and couple electromagnetically to the ground plane of the PWB. Such coupling can be both beneficial and detrimental. For instance, a quarter-wavelength antenna uses the ground plane of the PWB to increase the effective size of the antenna.
However, due to the shrinking nature of mobile phone design, radiation performance has become more troublesome to achieve. Especially at low frequencies, this is a growing problem, since the PWB acts like a dipole antenna and most of the radiation actually comes from the ground plane and not the antenna itself. The optimal length, for the low frequency bands, of the PWB is about 120-130 mm (millimeters), from a radiation performance point of view. This is however not acceptable from an industrial design point of view. For instance, 120 mm is about 4.7 inches, which is too long for many common mobile phones.
Therefore, it would be beneficial to provide techniques for improving radiation performance of antennas, to decrease the physical size of the antenna, or both.